Visual chromophores

Natural Sensitizing Dyes and Photodynamic Therapy. The chlorophylls are, of course, among the natural sensitizers for photosynthesis. Considerable iaterest exists ia chlorophyll and related pigments as photosensitizers ia biology and medicine (75), isomeric retinal chromophores as visual pigments (76,77), and the use of synthetic photosensitizers ia neurobiology (9), hematology (78), and photodynamic therapy (79). 

The complexes on surface of chelate-functionalized silica often include ligands available in solution in the coordination sphere. Use of a chromophore reagent as a ligand leads to the formation of colored mixed ligand complexes (MLC). The phenomena can be used as a basis for developing test-systems for visual determination of microquantities of inorganic cations in water. 

Apart from lutein and zeaxanthin, a number of other xanthophylls are present in the retina at low concentrations, including 3 -cpi-lutein, lactucaxanthin, 3 -dehydrolutein, and (3,(3-carotene-3,3 -dione (Khachik et al. 1997a, Bernstein et al. 2001). Interestingly, (3-carotene, the provitamin A precursor of the chromophore of the visual pigments, has only been identified in traces in the retina, if at all. 

Suzuki Y, Yokoyama K (2007) A protein-responsive chromophore based on squaraine and its application to visual protein detection on a gel for SDS-PAGE. Angew Chem Int Ed 46 4097 1099... 

Birge RR, Pierce BM (1979) A theoretical analysis of two-photon properties of linear polyenes and the visual chromophores. J Chem Phys 70 165-178... 

Rhodopsin is a seven ot-helix trans-membrane protein and visual pigment of the vertebrate rod photoreceptor cells that mediate dim light vision. In this photoreceptor, retinal is the chromophore bound by opsin protein, covalently linked to Lys296 by a Schiff base linkage. Kpega et al.64 have studied NMR spectra of Schiff bases being derivatives of all-frans retinal and amino-p-cyclodextrins as a model of rhodopsin, where p-cyclodextrin plays a role of a binding pocket. On the basis of analysis of the chemical shift differences for the model compound in the presence and in the absence of adamantane carboxylate, it has been shown that the derivative of 3-amino-p-cyclodextrin forms dimer in water and retinoid is inserted into p-cyclodextrin cavity [31]. 

Since the early 90s, noninvasive functional brain imaging of humans using NIR methods have been slowly gaining momentum despite existence of more established imaging modailties, such as PET, fMRI, and EEG. Part of the reason as stated previously, is because of its relatively high temporal resolution and its ability to monitor multiple tissue chromophores. The technique has been applied to adult as well as infant studies. NIR method is particularly suited for infant studies as the equipment, at least the CW kind, are minimally restraining, relatively safe, and portable [67]. Most neonatal studies focus on sensory stimulation such as visual, auditory and olfactory stimulations [69] [101] [89] [115] [6] [5], and cerebral disfunction [70, 71]. Our review will focus primarily on adult studies with some emphasis on defense and security applications. 

The orange color of the Co(III) chromophore (e 100 M 1 cnr1, 485 nm) allows ready visual detection. 

Foster In view of the concentration of chromophore in the visual system, a 500-fold reduction of chromophore in the eye may have very httle effect on the inner retinal photoreceptors. It is striking that Drosophila carotenoid-depletion experiments only reduce the visual ERG but did not abolish it. 

Foster I don t know the mechanism whereby chromophore is retained. The bottom line is that we know chromophore is only depleted in flies and mice, and that most of the retinoid will be part of the visual system anyway. There must be some other way of retaining vitamin A. In fact in mammals, there are a whole range of potential vitamin A binding proteins, hke IRBP in the pigmented epithelium, that could serve to mop-up and act as a chromophore sink. 

Ihee, H., Rajagopal, S., Srajer, V., Pahl, R., Schmidt, M., Schotte, R, Anfinrud, P. A., Wulff, M., and Moffat, K. 2005. Visualizing chromophore isomerization in photoactive yellow protein from nanoseconds to seconds by time-resolved crystallography. Pmc. Natl. Acad. Set, USA 102 7145-50. 

Photochemical cis-trans isomerization in a conjugated polyene system is thought to be the crucial primary process in vision. The visual pigment (rhodopsin) is derived from 11 -crs-retinal by reaction of the aldehyde group with an amino substituent in a protein (opsin). There is considerable distortion in the geometry of this chromophoric group anyway, because of the spatial requirements of the protein... 

Retinol A. can be enzymically formed from retinoic acid. B. is transported from the intestine to the liver in chylomicrons. C. is the light-absorbing portion of rhodopsin. D. is phosphorylated and dephosphorylated during the visual cycle. E. mediates most of the actions of the retinoids. Correct answer = B. Retinyf esters are incorporated into chylomicrons. Retinoic acid cannot be reduced to retinol. Retinal, the aldehyde form of retinol, is the chromophore for rhodopsin. Retinal is photoisomerized during the visual cycle. Retinoic acid, not retinol, is the most important retinoid. 

The all-trams forms of the vitamins A predominate but 11-c/s-retinal is the lightabsorbing chromophore of the visual pigments... 

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